1. Field of the Invention
The present invention relates to a dry toner for use in developing an electrostatic latent image formed by a method such as electrophotography and electrostatic recording. In addition, the present invention also relates to a toner kit containing the dry toner and an image forming apparatus and a process cartridge using the dry toner.
2. Discussion of the Background
When a polyester resin is used as a binder resin of toner, the resultant toner has the following advantages:    (1) The toner can be fixed by a heat roller fixing device at a relatively low fixing temperature (i.e., the toner has good low temperature fixability); and    (2) Even when the toner is fixed by a heat roller fixing device at a relatively high temperature, the toner does not cause a hot offset problem in that the toner image adhere to the fixing rollers, and the transferred toner image is re-transferred to a receiving material, resulting in formation of an undesired image (i.e., the toner has good hot offset resistance).
Therefore, polyester resins are typically used for toner.
Recently, electrophotographic color copiers and printers have been popularly used. Color copy images are required to have high gloss. In order to produce a color toner which has good hot offset resistance and which can produce color images having high gloss, using a polyester resin as the binder resin of the color toner is effective.
However, conventional toners including a polyester resin have a drawback in that toner particles adhere to each other when being agitated with an agitator in a developing device, resulting in formation of the aggregate of the toner particles. Particularly, since color toner includes a relatively large amount of polyester resin to produce glossy images, a relatively large amount of aggregated toner particles are formed.
In addition, recently a need for high definition images increases more and more. Therefore, toner having a relatively small particle diameter is typically used. Toner having a small particle diameter typically has poor resistance to heat, pressure and impact. Therefore, toner having a small particle diameter produces a relatively large amount of aggregated toner particles.
When toner is used for a two component developing method, the toner is aggregated by the compression pressure due to collision of carrier particles. In a case of one component developing method, toner is aggregated by the pressure applied thereto by a blade and/or the heat generated by friction between a developing roller (or the blade) and the toner, when a toner layer is formed on the developing roller. In both cases, the toner achieves a semi-fused state due to the heat generated by friction between the toner and agitators or screws in the developing device used, resulting in occurrence of the aggregation problem.
When an electrostatic latent image is developed with a two component developer including aggregated toner particles, the aggregated toner particles adhere to the latent image, resulting in formation of a toner image including a large spot having a high density. In addition, since the aggregated toner particles serve as a spacer in the toner image transfer process without being transferred, the transferred toner image has an omission.
When an electrostatic latent image is developed with a one component developer including aggregated toner particles, the aggregated toner particles are sandwiched by the developing roller and the blade used for forming the toner layer, resulting in formation of a white streak in the resultant image. Particularly, such an abnormal image is relatively highly visible in color images compared to black and white images. In addition, the requirements (e.g., half tone properties, color reproducibility and resolution) for color images are generally severer than those for black and white images. Therefore, the aggregated toner particles present big problems for color images.
Because of these reasons, a need exists for a toner which includes a polyester resin as a binder resin and which has good low temperature fixability and good hot offset resistance and can produce glossy images without causing the above-mentioned undesired image problems.